The polyphenylene ether resins are a family of engineering thermoplastics that are well known to the polymer art. These polymers may be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos, 3,306,874 and 3, 306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes for preparing polyphenylene ether resins, including graft copolymers of polyphenylene ethers with styrene type compounds, are found in Fox, U.S. Pat. No. 3,356,761; Sumitomo, U.K. Pat. No. 1,291,609; Bussink et al, U.S. Pat. Nos. 3,337,499; Blanchard et al, 3,219,626; Laakso et al, 3,342,892; Borman, 3,344,116; Hori et al, 3,384,619; Faurote et al, 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are known from patents such as Wieden et al, U.S. Pat. Nos. 3,442,885 (copper-amidines); Nakashio et al, 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al, 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as a peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al., 3,382,212. All of the above-mentioned disclosures are incorporated herein by reference.
Compositions including a polyphenylene ether component can be chemically and physically combined, and they can be in liquid media in the form of emulsions, solutions, suspension solution combinations, e.g., as disclosed in U.K. Pat. No. 1,291,609, incorporated herein by reference, and the like. Among the most important of such compositions are compositions of polyphenylene ethers with alkenyl aromatic resins, including rubber-modified polystyrene resins, and graft copolymers of polyphenylene ether resins with alkenyl aromatic resins, including styrene homopolymer resins, and the like. These are described, for example, in Cizek, U.S. Pat. No. 3,383,435, which is incorporated herein by reference.
Compositions of polyphenylene ethers and polystyrene or rubber-modified polystyrene can also be prepared by the oxidation of the corresponding phenol, e.g., 2,6-dimethyl phenol in a solution of polystyrene or rubber-modified polystyrene. See, for example, Katchman, U.S. Pat. No. 3,663,661, the disclosure of which is incorporated herein by reference. Reaction mixtures containing graft copolymers of polyphenylene ether resins and styrene resins can also be made by polymerization of vinyl aromatic monomers in the presence of polyphenylene ethers according to, for example, the disclosure of Fox, Canadian Pat. No. 785,834, which is incorporated herein by reference.
In general, all of the above processes produce the polyphenylene ether or resinous composition as a component in a liquid medium, and a common subsequent step is to add a polymer non-solvent to the liquid medium to precipitate the polymer. For example, if the resinous composition is combined in a medium which includes benzene, toluene, xylene, or the like, adding methanol will precipitate the polyphenylene ether. If the resinous composition is in pyridine, adding water will precipitate the resinous composition.
In commonly assigned U.S. patent application Ser. No. 311,837, filed Dec. 4, 1972, now abandoned, incorporated herein by reference, it was disclosed that a composition comprising polyphenylene ether resin can conveniently be isolated from a liquid medium, if one of the liquid components is steam-distillable, by slowly adding to hot water with vigorous agitation. Under these conditions, the steam-distillable component is rapidly removed by steam-distillation, leaving the composition in the form of a friable, easily pulverized, crumb which is suitable after drying for extrusion, compression molding, and the like. Compositions made from rubber-modified polystyrene in combination with polyphenylene ether resin produced by this process have good impact strength and other physical properties but poor color, i.e., they are highly colored. Attempts to reproduce these results with reaction mixtures produced on a commercial scale were unsuccessful as the resulting product had poor color and, when blended with rubber-modified polystyrene, yielded a resin with poor color and with greatly reduced impact strength.
The crumbing process itself, applied to solutions of purified polyphenylene ethers, does not cause reduced impact strength or poorer color when the product is compounded with rubber-modified polystyrene, nor does addition of the low molecular weight by-products, separately isolated, to compositions comprising the polyphenylene ether and the rubber-modified polystyrene cause significant reduction in impact strength. Furthermore, when the polyphenylene ether is isolated from reaction mixtures containing the by-products by total isolation procedures which do not involve water, for example, by spray-drying in a nitrogen atmosphere, compositions with polystyrene do not have reduced impact strength, although color and thermal-oxidative stability are adversely affected. Decolorization by hydrogenation or chemical reduction prior to crumbing can yield products of good color, but usually with lowered impact strength.
It has been found that by combining the heating procedure described herein with intrinsic viscosity stabilization techniques such as those disclosed in Yonemitsu et al., U.S. Pat. No. 3,970,640 and Cooper et al., U.S. Pat. No. 4,110,311, both incorporated herein by reference, crumbed polyphenylene ether resin compositions can be consistently produced which result in compositions also comprising rubber-modified polystyrene, that have excellent impact strength and thermal-oxidative stability and that have tensile strength, heat distortion temperature, and other physical properties equivalent to those of similar compositions comprised of methanol-precipitated polyphenylene ether resin compositions.
The color of the polymer isolated by hot water crumbing after heating in the presence of the stabilizer is better than that of the polymer similarly isolated with no thermal treatment, but inferior to that of polymers isolated by precipitation with methanol or of polymers isolated by crumbing after heating without stabilizer present. Surprisingly, however, compositions comprising rubber-modified polystyrene and polyphenylene ether isolated by hot water crumbing after heating in the presence of the stabilizer have better color than similar compositions made from polyphenylene ether isolated by methanol precipitation without treatment or by crumbing after heating without stabilizer. The color of the first-mentioned compositions is not stable, however, and a green tint develops within a few days. Compositions which were initially white become a light olive color in four to six weeks. Exposure to ultraviolet light such as is provided by a fluorescent blacklight lamp, causes a pronounced pink color within a few hours. The product is, therefore, not suitable for use in white or light-colored formulations where color stability is important.
It has been found that, where color stability is important, it is advisable to add, as a final step prior to crumbing, a capping reaction whereby phenolic hydroxyl groups are converted to acetate groups or other stable groups. Capping need not be complete; compositions made from crumbed polyphenylene ethers in which only two-thirds of the polymeric hydroxyl groups had been capped showed complete color stability, with no detectable change over a period of more than a year. Apparently the structures responsible for color instability react preferentially with the capping agents. Initial colors of the compositions made from polymer crumbed after partial capping are also improved, as well as stability to ultraviolet light. No pink color develops on exposure to fluorescent blacklight, and the rate of photoyellowing is slower than that of compositions made from methanol-precipitated polymers.
It is, therefore, a primary object of this invention to provide an improved method of isolating polyphenylene ether resins by crumbing in hot water.
Another object of this invention is to provide molding compositions and molded articles that are based on polyphenylene ether resins produced by crumbing in hot water and that have improved thermal oxidative stability.
Still another object of this invention is to provide molding compositions and molded articles that are based on polyphenylene ether resins produced by crumbing in hot water and that have improved impact strength.
It is also an object of this invention to provide the above-described, improved molding compositions in reinforced and/or flame-retardant embodiments.